Method for processing output or base signals from a device for determining a distance of an object

ABSTRACT

To provide a method of processing output or base signals (S), in particular intermediate frequency output or base signals, from at least one device, in particular at least one radar device, for determining a distance (d), in particular a small distance on the order of magnitude of approximately zero meters to approximately 7 meters, of an object, by which it is possible to obtain from the raw signals, i.e., the output or base signals, distance information with respect to at least one object located in the detection or sensing range of the device, the following steps are provided:
     (a) Adaptively determining the background signal (S 0 ) by localized filtering of the output or base signal (S) using at least one localized filter having a specified width (B);   (b) Correcting the background of the output or base signal (s) by   (b.1) subtracting the determined background signal (S 0 ) from the output or base signal (S) and   (b.2) forming a signal, in particular (s=abs (S−S 0 )), for example, from the difference (S−S 0 ) of the output or base signal (S) and the background signal (S 0 );   (c) Low-pass filtering, in particular temporal low-pass filtering, of the absolute value signal (s);   (d) Forming a correlation signal (k=korr(s)) by correlating, in particular folding, the low-pass filtered absolute value signal (s) with at least one reference maximum having a half-value width; and   (e) Determining the at least one object maximum (M) using at least one location-variable, adaptive threshold value (t) which may be determined from the correlation signal (k).

FIELD OF THE INVENTION

The present invention relates to a method of processing output or basesignals, e.g., intermediate frequency output or base signals, from atleast one device, e.g., at least one radar device, for determining adistance, e.g., a small distance on the order of magnitude of the closerange of a vehicle, of an object.

BACKGROUND INFORMATION

In short range radar (SRR) systems, i.e., in radar devices fordetermining a small distance, there are various methods for processingand evaluating output or base signals. One method, for example, is basedon a threshold value algorithm, taking into account a background signalwhich is assumed to be constant, and taking into accountdistant-dependent, fixed threshold values.

However, for objects present which are to be detected or sensed by SRRsystems and which move at a high relative velocity, this can result inexceedance of the threshold values at positions where objects are notpresent.

Such phenomena, which may be subsumed under the concept of the parasiticDoppler effect, result in undesired malfunctions and/or erroneousinformation. Furthermore, malfunctions and/or erroneous information mayalso be caused by intrinsic phenomena such as aging effects ortemperature influences.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method by which it ispossible to obtain from the raw signals, i.e., the output or basesignals, from at least one device, e.g., at least one radar device,distance information with respect to at least one object located in thedetection or sensing range of the device.

In this context, an object of the present invention is to process theoutput or base signals in such a way as to minimize the influence ofchanges in the output or base signals on the signal amplitudes to beevaluated with respect to the maximum or peak positions.

Consequently, the exemplary method of the present invention alsoprovides a method by which the accuracy of detection may be increasedunder all conditions.

These objects may be achieved according to the exemplary embodiments ofthe present invention.

According to the exemplary method of the present invention, a robustmethod of processing output or base signals from a device fordetermining a distance of an object is provided which is substantiallyindependent of extrinsic effects (for example, a parasitic Dopplereffect when objects having a high relative velocity are present) andintrinsic effects (for example, aging phenomena or temperatureinfluences).

In this context, complicated modifications or changes to the systemcomponents in the high-frequency part for suppressing the parasiticDoppler effect or for increasing the accuracy of detection in manyapplications and operational areas, such as parking aids or pre-crashdetection systems, may be dispensed with.

Lastly, the present invention relates to a device, e.g., a radar device,for determining a distance, e.g., a small distance on the order ofmagnitude of the close range of a vehicle, of an object, which operatesaccording to the method described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram in which a progression of an intermediatefrequency output or base signal at the mixer output of a microwavedetector device is plotted against the distance of the object.

FIG. 2 shows a diagram in which a progression of an intermediatefrequency output or base signal at the mixer output of a radar devicefor a structured background signal is plotted against the distance ofthe object.

FIG. 3 shows a diagram in which the curve is plotted for theintermediate frequency output or base signal according to FIG. 1 or 2after digital-to-analog conversion.

FIG. 4 shows a diagram in which the progression of the absolute valuesignal from the difference between the output or base signal and thebackground signal is plotted against the distance of the object.

FIG. 5 shows a diagram in which the progression of the correlationsignal formed by correlating, e.g., multiplying, the low-pass filteredabsolute value signal according to FIG. 4 by a reference maximum havinga half-value width is plotted against the distance of the object.

FIG. 6 shows a diagram in which the progression of the signal at amaximum, which is determined using a location-variable, adaptivethreshold value that may be determined from the correlation signalaccording to FIG. 5, is plotted against the distance of the object.

DETAILED DESCRIPTION

With reference to FIGS. 1 through 6, an exemplary embodiment isillustrated for a method of processing intermediate frequency output orbase signals S, which may also be described as intermediate frequencyraw signals, using a microwave detector device (see FIG. 1) or a radardevice for a structured background signal S₀ (see FIG. 2).

Using this method, a distance d of an object may be determined, forexample, when parking a motor vehicle, the distance from the curb or thedistance of the bumper from the motor vehicle parked in front or behind.In this context, using the exemplary method according to the presentinvention, small distances in the approximate vicinity of a vehicle,e.g., from about zero meters to about 30 meters, may be determined.

FIGS. 1 and 2 show some characteristics of intermediate frequency outputor base signals S (raw signals). These raw signals are present in alow-voltage range, e.g., in an output voltage range of fromapproximately zero volts to approximately 5 volts, the average valuebeing, e.g., approximately 2.5 volts. Background signals S₀, i.e., thesignals in the absence of objects, may have a different average valueand a more or less strongly pronounced structure, depending on the typeof sensor device (e.g., sampling phase detector device in FIG. 1 orradar device in FIG. 2).

In this context, the short range radar (SRR) system functions as asampling phase detector device (a phase-dependent pulse radar device);i.e., the distance maxima are cancelled for the intermediate frequencyas a function of the distance from the object to be detected (see FIG.1). Positive and negative maxima each result in cancellations atdistances of one-fourth wavelength (λ/4), in other words, at distancesof approximately 3 millimeters at a carrier frequency of, e.g.,approximately 24 Gigahertz.

Specified portions may be superimposed on intermediate frequency outputor base signal S (raw signal) by extrinsic phenomena, such as theparasitic Doppler effect (see FIG. 2), and/or by intrinsic phenomenasuch as aging effects or temperature influences, with the result thatbackground signal S₀ may be very highly structured.

According to the exemplary method, the digitalized voltage values ofintermediate frequency output or base signal S from the sampling phasedetector device first undergo a digital-to-analog conversion beforebackground signal S₀ is adaptively determined by localized filtering ofoutput or base signal S, using a localized median filter of a specifiedwidth B. According to FIG. 1, object maximum M marked by the arrowexhibits a “backswing response” at “1” due to the sampling phasedetector device; at “2” the object is displaced by one-half wavelength(λ/2) with respect to “1”. In FIG. 2, object maximum M marked by thesingle arrow is located on the structured background caused by theparasitic Doppler effect; fixed, distance-dependent threshold values aremarked by the double arrow.

To this end, multiple, for example eleven, voltage values for output orbase signal S are measured at a specified time over the spectrum,sorted, and the median (as the value in the middle of the window) isselected, width B of localized median filter being adjusted to themaximum width in output or base signal S for the object (see FIG. 3). Bythis formation of median or average values, object maximum M may beidentified (see FIG. 3) and “interfering” maxima are eliminated.

The background for output or base signal S is subsequently corrected. Tothis end, background signal S₀, determined using the localizedfiltering, is subtracted from output or base signal S, and absolutevalue signal s=abs (S−S₀) is formed from difference S−S₀ of output orbase signal S and background signal S₀. This absolute value formationtakes into account the fact that the signal amplitude may fluctuateabout the average value due to the properties of the sampling phasedetector device, and thus has the advantage that the correction isreliably made even with variable background signals S₀ (for a “fixed”constant background, an overall difference may also be formed).

To increase the accuracy of detection under all conditions for thepresent method, after the background is corrected, temporal low-passfiltering is provided for the absolute value signal s produced. To thisend, the positive portions and the negative portions of absolute valuesignal s produced are summed over multiple measurement cycles, thetemporal low-pass filtering being carried out by a floating averagevalue filter having a specified time constant.

Subsequently, for peak amplification, i.e., for amplifying the maximumaccording to FIGS. 4 and 5, a correlation signal k=korr(s) is determinedby correlating, in the case of the present embodiment by folding,low-pass filtered absolute value signal s with a reference maximumhaving a half-value width.

In the subsequent peak detection, i.e., in the determination of the peaklocations, object maximum M is determined using a location-variable,adaptive threshold value t (see FIG. 6) which may be determined fromcorrelation signal k (see FIG. 6), location-variable, adaptive thresholdvalue t being acted on by a distance-dependent offset value Δ (see FIG.6).

To now obtain the actual distance of the object, the peak location,i.e., the position of object maximum M is associated with a specifieddistance d of the object using a characteristic curve determined throughcalibration. Consideration should be made for the fact that therelationship between the signal peak and the distance of the object orof resolution cells (to be briefly described below) is not linear,therefore the calibration characteristic curve may be determined.

This is carried out or performed using resolution cells; i.e., theregion for determining distance d of the object is subdivided into aspecified number of cells, for example into 2⁸=256 cells (8 bits), whichin the embodiment of the present method provide reference measurementsin 256 levels; consequently, it is possible to conveniently determine inwhich of the 256 resolution cells the object is located.

1. A method for processing an intermediate frequency signal from atleast one device for determining a distance of an object, the methodcomprising: adaptively determining a background signal by providinglocalized filtering of the signal using at least one localized filterhaving a specified width; correcting a background of the signal bysubtracting a determined background signal from the signal, and formingan absolute value signal from an absolute value of a difference betweenthe signal and the background signal; low-pass filtering the absolutevalue signal; forming a correlation signal by correlating the absolutevalue signal with at least one reference maximum having a half-valuewidth; and determining at least one object maximum using at least onelocation-variable, adaptive threshold value which is determinable fromthe correlation signal.
 2. The method of claim 1, wherein theintermediate frequency signal includes an output signal.
 3. The methodof claim 2, wherein the intermediate frequency signal includes a basesignal.
 4. The method of claim 1, wherein the device includes a radardevice.
 5. The method of claim 1, wherein the distance is a smalldistance on the order of magnitude of a close range of the vehicle. 6.The method of claim 1, wherein the distance is in a range fromapproximately zero meters to approximately 30 meters.
 7. The method ofclaim 1, wherein the low-pass filtering includes temporal low-passfiltering.
 8. The method of claim 1, wherein the correlating isperformed by folding a filtered absolute value signal with the at leastone reference maximum.
 9. The method of claim 1, further comprising:providing digital-to-analog conversion of the signal before thebackground signal is adaptively determined.
 10. The method of claim 1,wherein the localized filtering of the signal at a specified time isperformed by measuring, sorting, and selecting an average value fromvoltage values over a spectrum.
 11. The method of claim 10, whereineleven (11) voltage values are used.
 12. The method of claim 1, whereinthe signal is locally filtered using at least one median filter.
 13. Themethod of claim 1, further comprising: adjusting a width of thelocalized filter to a width of the object maximum of the signal for theobject.
 14. The method of claim 1, wherein the absolute value signal islow-pass filtered by summing portions in the absolute value signal overdetermination cycles.
 15. The method of claim 1, wherein the low-passfiltering is performed using at least one average value filter having aspecified time constant.
 16. The method of claim 15, wherein the averagevalue filter is a floating average value filter.
 17. The method of claim1, wherein the location-variable, adaptive threshold value is acted onby at least one distance-dependent offset value.
 18. The method of claim1, wherein the object maximum is associated with a specified distance ofthe object using at least one characteristic curve determined bycalibration.
 19. The method of claim 1, wherein a range for determiningthe distance of the object is subdivided into a specified number ofcells.
 20. The method of claim 19, wherein the specified number of cellsis 2⁸ (256) using 8 bits.
 21. A radar device to determine a distance,which is a small distance on the order of magnitude of a close range ofa vehicle, of an object, comprising: an adaptive determining arrangementto adaptively determine a background signal by providing localizedfiltering of the signal using at least one localized filter having aspecified width; a correcting arrangement to correct a background of thesignal by subtracting a determined background signal from the signal,and forming an absolute value signal from an absolute value of adifference between the signal and the background signal; a low-passfiltering arrangement to low-pass filter the absolute value signal; acorrelating arrangement to form a correlation signal by correlating theabsolute value signal with at least one reference maximum having ahalf-value width; and a determining arrangement to determine at leastone object maximum using at least one location-variable, adaptivethreshold value which is determinable from the correlation signal.